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-   -   too much valve clearance? (http://forums.pelicanparts.com/911-engine-rebuilding-forum/532199-too-much-valve-clearance.html)

robmog 03-20-2010 05:49 PM

too much valve clearance?
 
during my stock 72 2.4 E rebuild:
deck clearance 1.5mm
set cam timing as per specs.
the CLOSEST my valves came to the piston was 5 mm.
i know too close (intake 1.5mm, exhaust 2mm) is bad,
but can you have too much clearance?
does 5mm sound reasonable for a stock E cam with stock E pistons?

kenikh 03-23-2010 05:01 PM

No clue, but as long as your deck height is right, your valves are adjusted right and your heads cc out OK, I don't see why it is an issue. The E cam is not high lift and the E was designed with lower compression in mind, so those domes aren't going to rise very high into the chamber.

robmog 03-23-2010 05:08 PM

thanks kenik.
i'm suffering from rebuild paranoia.
as the $$$ goes up so does my anxiety!

Eagledriver 03-27-2010 08:41 PM

I have two points about this. The first is that your deck height is kind of high. This engine is a low compression engine so I would run it at 1mm deck height to maximize your compression. The second point is about your valve to piston clearance. Are you measuring at TDC? If so you are not measuring the closest clearance. This is a common misconception. Closest clearance for the exhaust valve is before TDC and for the intake valve is after TDC. How much before and after depends on the engine. I'd measure at 5 degrees and 10 degrees.

With the 5mm number you found, I wouldn't bother measuring at the other numbers. You have plenty of clearance.

-Andy

robmog 03-28-2010 07:37 AM

At TDC the clearance is 5.75mm.
the deck height # may be a bit off (high) i had to use clay, the solder trick wouldn't work for me.
even if i swap out my cylinder base gaskets, how much extra compression is a .5 mm decrease gonna get me.
i was wondering if any rebuilders out there have seen these #'s. i'm not building a race car.
but maybe not too many are using stock e cams.
thanks

Eagledriver 03-28-2010 07:42 PM

In a 2.7 engine .5mm gives about a half point compression increase.

-Andy


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